The geology consists of Triassic-aged, low permeability siltstone and shale bedrock. Porosity is estimated at 1-4%. Groundwater flow appears to be controlled by horizontal bedding fractures and the regional strike direction.
Targeted Environmental Media:
 Dense Non-aqueous Phase Liquids (DNAPLs) - Fractured Bedrock
The main source area is located in shallow bedrock to a depth of approximately 40 ft bgs, some deeper contamination is observed. The lateral extent is approximately 80 ft by 120 ft. The dissolved PCE plume was approximately 4,000 ft in length prior to treatment.
The detection of PCE degradation products at significantly lower concentrations indicated reductive dechlorination was occurring. The detection of ethene at concentrations of 9 and 450 micrograms per liter confirmed the complete degradation of PCE to non-chlorinated compounds.
Major Contaminants and Maximum Concentrations:
- Tetrachloroethene (~240000)
- Borehole Geophysics
- Caliper
- Acoustic Televiewer
- Fluid Loggings
- Temperature
- Conductivity/Resistivity
- Flow
- Vertical Chemical Profiling
- Packer Isolation
- Multi-sampling port
- Coring
- Fracturing
- Pump and Treat
- Bioremediation (In Situ)
- Reductive Dechlorination (In Situ Bioremediation)
- Other (Nanoscale zero valent iron)
Comments:
The remedial approach at the site has consisted of several technologies to address both off-site migration and source contamination. Trends at the site are indicative of complete dechlorination occurring with decrease of total molarity at most performance monitoring wells.
Initial remediation efforts included operation of a pump and treat system to mitigate/control off-site transport. Following initial operations of the pump and treat system, an enhanced bioremediation system was installed at the property to provide containment. The system consisted of two lines of electron donor injection wells at the property boundary. Molasses is the electron donor.
Initial data from the bioremediation system indicated that injections of molasses created a strongly reduced environment (less than -250 mV ORP). Increased organic carbon concentrations were observed resulting in an enhanced anaerobic environment, increases in metabolic activity as evidenced by the production of by-products such as methane, and an enhanced reductive dechlorination rate. During the first four months of operation, PCE was reduced by approximately 97%. With the approval of the regulatory agency, the pump and treat system was permanently decommissioned, and enhanced bioremediation via molasses injection operations continued.
Successful plume cut-off has been achieved and the bioremediation system continues to operate as of Dec 2005.
In addition to the bioremediation treatment at the property line, enhanced bioremediation via molasses injection was also implemented in the contaminant source area. The objective of this activity was to treat source mass and shorten the overall remediation timeframe. Molasses injections began in the source area in 2001, and complete dechlorination to ethene was consistently observed. A robust dechlorinating community is present, supported by regular molasses injection.
-prevent off-site contaminant migration
-aggressively treat contaminant source
While source area molasses injections continued, nanoscale zero valent iron was completed as a more aggressive approach for source area remediation. A pilot test of nanoscale ZVI was conducted in 2003, and (with the approval of the regulatory agency) full scale activities were performed in late 2005. Injection of approximately 800 lb of nanoscale ZVI was performed in 4 injection wells in the shallow source area in Nov-Dec 05. Fracturing was performed prior to ZVI injection in order to improve hydraulic communication and the ability to distribute ZVI throughout the source area. Performance monitoring of the ZVI injection indicated significant impacts on source area geochemistry, including increased pH levels (~9) and low ORP values (-500 mV). Currently molasses injections are conducted on a bimonthly frequency focusing on the source area and areas of contaminant flux.
The combination of molasses injections and ZVI provided an abiltiy to enhance mass reduction at the source area. Fracturing of the source area prior to full scale increased contact with contaminant mass. Downgradient flux can be addressed efficiently by having a flexible network of injection wells to address where contaminant migration is occurring.
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